Heritage timbers

The UK has a large number of historic buildings which contain timber frames, roofs, floors or cladding and the important ones fall within conservation legislation. However, the majority of historic buildings are covered by the same planning regulations as modern buildings. Over time, poor maintenance and inappropriate repair and conservation treatments can lead to the accelerated decay of the building fabric.

The process of selecting replacement timber involves a small amount of analysis of original material, but ultimately this information is inadequate. The performance of replacement timber is rarely monitored following the repair work and as such little is known about how the selected replacement will integrate itself into the building over time. FPRI is working with Historic Scotland to develop simple and low cost methods of assessing the mechanical and physical properties of historic timber that will, in future, allow for more informed conservation practices. Historic Scotland is an executive agency of the Scottish Government and are charged with safeguarding the nation's historic environment and promoting its understanding and enjoyment.

Acoustic non-destructive testing has been extensively used within FPRI's Strategic Integrated Research in Timber (SIRT) project, where different techniques have been applied for predicting the structural quality (primarily static strength and stiffness) of modern timber at various stages in the wood-chain from tree to sawn dry timber. However, this work has shown that the correlations between the dynamic and the static mechanical and physical properties vary, due to environmental and silvicultural influences on tree growth. It is, therefore, to be expected that the correlation for historic timber cannot be assumed from correlations obtained on modern timber. It is also useful to investigate the extent to which the difference in correlation is due to aging degradation (i.e. changes at the microstructural level) and to what extent due to the radically different environment in which the trees grew. Therefore, the study of historic timber provides an opportunity to look at the potential for improving wood quality in modern timber through altered forestry practices.

The work combines measurement of the dynamic mechanical properties of timber in situ and in a laboratory environment (both historic and artificially aged wood) as well as a comprehensive series of destructive mechanical and physical chemistry tests on a small sample of mediaeval timber. The research also includes investigation of dynamic vapour sorption, swelling and creep.

Some of the work was undertaken with the assistance of a visiting researcher with expertise in the physical chemistry techniques for restoration and preservation of cultural heritage wooden artefacts. Dr. Carmen-Mihaela Popescu of the "Petri Poni" Institute of Macromolecular Chemistry, Iasi Romania, stayed for a period of two months at FPRI. This was supported with funding from the project PERFORM-ERA "Postdoctoral Performance for Integration in the European Research Area" (ID-57649), financed by the European Social Fund and the Romanian Government.

The picture shows ultrasonic measurement of the Prestongrange Ceiling (1581) in Merchiston Tower